CVE-2021-20263 : Security Advisory and Response

A flaw was discovered in the virtio-fs shared file system daemon (virtiofsd) of QEMU, potentially allowing a malicious user to elevate their privileges within the guest.

Understanding CVE-2021-20263

This CVE identifies a vulnerability in the 'xattrmap' option of the virtio-fs shared file system daemon (virtiofsd) of QEMU. The flaw could be exploited to create a modified, privileged executable in the guest.

What is CVE-2021-20263?

The vulnerability in the 'xattrmap' option of the virtio-fs shared file system daemon (virtiofsd) of QEMU may lead to the 'security.capability' xattr not dropping on file write within the guest, potentially enabling elevation of privileges by a malicious user.

The Impact of CVE-2021-20263

In certain circumstances, this flaw could be utilized by a malicious actor to escalate their privileges within the guest operating system, posing a significant security risk to the affected systems.

Technical Details of CVE-2021-20263

This section provides more in-depth technical insights into the vulnerability.

Vulnerability Description

The flaw allows the 'security.capability' xattr in the guest to not drop on file write, facilitating the creation of a modified, privileged executable within the guest OS.

Affected Systems and Versions

The vulnerability affects QEMU version 5.2.50 with the 'xattrmap' option enabled, potentially impacting systems utilizing this specific configuration.

Exploitation Mechanism

Malicious users could exploit this vulnerability to retain the 'security.capability' xattr, leading to the creation of a modified executable that could elevate their privileges within the guest operating system.

Mitigation and Prevention

To address CVE-2021-20263 and enhance system security, immediate and long-term actions should be taken.

Immediate Steps to Take

It is recommended to disable or restrict the usage of the 'xattrmap' option in the virtio-fs shared file system daemon (virtiofsd) of QEMU. Additionally, monitoring for any unusual file modifications can help detect potential exploitation attempts.

Long-Term Security Practices

Implementing the principle of least privilege, regular security audits, and keeping software up to date are essential long-term security practices to mitigate the risk of privilege escalation vulnerabilities.

Patching and Updates

Ensure that the affected QEMU version 5.2.50 is updated with the necessary patches provided by the vendor to address the vulnerability and enhance system security.